The invention relates to a method and apparatus for controlling flux in an alternating current (AC) motor and, specifically, to a method and apparatus for accelerating flux to a nominal operating value in a coordinated manner without the need for flux feedback from the motor.
Control of an asynchronous AC motor is often achieved by directly or indirectly controlling motor flux. Conventionally, flux control requires determining the value of flux by measuring, for example, stator voltage and current and then deducing the motor flux from the measured voltage and current in combination with characteristics of the motor. For example, U.S. Pat. No. 5,172,041 to Bavard et al. discloses a method for asynchronous motor control using a closed-loop variation of magnetic induction flux as a function of a desired value. The motor flux is determined by detecting the motor voltage and the motor current and determining flux value by using the measured values in a motor operating equation.
U.S. Pat. No. 5,194,797 to Kahkipuro discloses a method for regulation of the stator flux and torque of an asynchronous motor using vector control. The absolute value of the stator flux is regulated by the real part of the stator voltage vector and the torque is regulated by the stator frequency. By adjusting the imaginary part of the stator voltage vector, the calculation coordinates are held in a position which allows the rotor flux to remain close to the real axis. The value of the torque and the absolute value of the stator flux are obtained by using measured parameters in a motor equation that is characteristic of the operation of the motor.
A first aspect of the invention is a preflux forcing controller for an asynchronous, alternating current (AC) induction motor drive system comprising means for generating a flux reference value, means for generating a flux boosting value, means for generating a preflux current value, means for processing the flux reference value, the flux boosting value, and the preflux current value to determine an output signal, and means for providing at least one command signal to the motor based on the output signal.
A second aspect of the invention is a method of forcing flux in an asynchronous, alternating current (AC) induction motor drive system comprising the steps of generating a flux reference value, generating a flux boosting value, generating a preflux current value, processing the flux reference value, the flux boosting value, and the preflux current value to determine an output signal, and providing at least one command signal to the motor based on the output signal.
A third aspect of the invention is a preflux forcing controller for an asynchronous, alternating current (AC) induction motor drive system comprising a command flux generator configured to generate a flux reference value, a flux boost generator configured to generate a flux boosting value, a preflux current generator configured to generate a preflux current value, processing circuitry configured to process the flux reference value, the flux boosting value, and the preflux current value to determine an output signal, and a current regulator and voltage feedforward model of a motor drive configured to provide voltage commands based on the output signal.
A fourth aspect of the invention is a motor drive system for an asynchronous, alternating current (AC) induction motor comprising a command flux generator configured to generate a flux reference value, a flux boost generator configured to generate a flux boosting value, a preflux current generator configured to generate a preflux current value, processing circuitry configured to process the flux reference value, the flux boosting value, and the preflux current value to determine an output signal, a current regulator and voltage feedforward model of a motor drive configured to provide voltage commands based on the output signal, a DC bus, a voltage regulation and DC bus compensation module coupled to an output of said flux current model module and configured to generate a voltage signal and a phase angle signal, a vector rotate and pulse width modulation module coupled to an output of said voltage regulation and DC bus compensation module and configured to generate switching signals based on the voltage signal and the phase angle signal an inverter having bridges disposed across said DC bus and being coupled to said vector rotate and pulse width modulation module to generate a voltage signal intended to induce a desired current in an AC induction motor based on the switching signals, and a motor coupled to an output of said inverter.